Use ScopedTaskEnvironment instead of MessageLoop in components unit tests.

components/sync/js/sync_js_controller_unittest.cc

Index: components/sync/js/sync_js_controller_unittest.cc
diff --git a/components/sync/js/sync_js_controller_unittest.cc b/components/sync/js/sync_js_controller_unittest.cc
index 51622c09f2e934c6177fe21195bc9f57239128d9..a96c92d58b7be776b5acbcbe02955bd274b160e0 100644
--- a/components/sync/js/sync_js_controller_unittest.cc
+++ b/components/sync/js/sync_js_controller_unittest.cc
@@ -5,6 +5,7 @@
 #include "components/sync/js/sync_js_controller.h"
 
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/values.h"
 #include "components/sync/js/js_event_details.h"
 #include "components/sync/js/js_test_util.h"
@@ -24,7 +25,7 @@ class SyncJsControllerTest : public testing::Test {
   void PumpLoop() { base::RunLoop().RunUntilIdle(); }
 
  private:
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 };
 
 TEST_F(SyncJsControllerTest, Events) {